Vapor generator steam temperature control



July 12, 1966 J, BLASKOWSKI 3,260,244

VAROR GENERATOR STEAM TEMPERATURE CONTROL Filed Dec. 30, 1963 United States Patent 3,260,244 VAPOR GENERATOR STEAM TEMPERATURE CONTROL Henry J. Blaskowski, Simsbury, Conn., assignor to Combustion Engineering, Inc, Windsor, C0nn., a corporation of Delaware Filed Dec. 30, 1963, Ser. No. 334,518 14 Claims. (Cl. 122-33} This invention relates to steam generators and particularly to a method and apparatus for the regulation of vapor generator vapor temperature therein.

It is desirable to control steam temperatures within steam generators since high temperatures have a deleterious effect on the heating surface and other pressure parts, while low temperatures degrade the plant heat rate. This is true not only on simple superheat, single and multiple reheat units, but also on once-through units of both the subcritical and supercritical type.

There are numerous factors in the design of steam generators which do not lend themselves to exact analysis. There must therefore be a means to adjust steam temperature in suflicient amounts to overcome this ignorance factor. Furthermore during operation of the unit a great number of conditions change from time to time and compensation must be made for the effects of these conditions. This includes variables such as slag and ash buildup on boiler tubes, soot blowing, cutting feedwater heaters out,'and changes in fuel quality. On occasions steam generators when put into service are found to operate with steam temperature consistently above or below the predicted value. In these cases extensive and expensive alterations are made, usually in the form of removing heating surface, in order to bring the temperature into line.

Insofar as steam temperature control is concerned, a vapor generator may be considered as divided into a number of independent sections. The first, or evaporator section comprises the normal economizer feedwater heating stage and the evaporating stage which is normally the furnace walls. These stages co-act absorbing suflicient heat to preheat and evaporate the desired steam quantity. The second independent section is the steam super-heating section wherein the quantity of steam evaporated is heated section is independent, its heat requirements being dicto the desired temperature. In heat units each reheater tated by the steam flow returning from the turbine as well as the reheater inlet steam temperature and the desired outlet steam temperature.

Types of steam temperature control within steam generators can be said to fall Within three groups. The first method involves the redistribution of neat to the various sections of the steam generator by means such as tilting burners or gas recirculation. In this mode of operation the heat being transferred to each section is actually varied to obtain the desired steam temperatures. A second type of control involves the distribution of the fluid being heated such as in spray desuperheating. Where evaporation is taking place in a first section and superheating in the second section, spray desuperheating actual- 1y involves bypassing this water around the evaporating section and evaporating the water being sprayed in the superheating section, thereby making use of the excess heat being absorbed by the superheater to evaporate water. A third type of steam temperature control involves exchanging heat directly between the fluid of the several sections being controlled. This involves apparatus such as the superheater to steam reheat steam heat exchanger. It should be remembered that in each of these modes of steam temperature control the heat input to the unit remains essentially constant since the desired heat output is a fixed value. These mehods of steam temperature control involve therefore only a redistribution of this fixed 3,260,244 Patented July 12, 1966 heat input and not a change of the actual heat input. Although as a practical matter controls may occasionally be operated to vary fuel feed to match steam temperature, this is only a convenient method of control. Any disturbance experienced in fuel input is merely a transient and the heat input returns to its original value thereafter.

Where steam temperature control by the distribution of heat is employed in a reheat unit the usual method involves surfacing the reheater and superheater to match steam temperature at full load, and designing into the unit a characteristic wherein during operation at reduced load distribution of heat to hold reheat temperature causes an excessive amount of heat to be absorbed in the superheater, and a deficiency of heat to be absorbed in the evaporating section. Spray desuperheating is employed in the superheater, bypassing water around the evaporative section and holding down the superheat temperature. High steam temperatures on both the reheater and superheater are normally obtained by increasing the gas temperature leaving the furnace, which is then entering the convection steam heating surfaces, and therefore the superheater and reheater temperatures are effected similarly. Since there is a practical limit to the ability to increase gas temperature leaving a given physical furnace, it would be preferable to transfer this excess heat in the superheater to the reheat steam, rather than dissipate it with spray, so that the control range of the unit could be extended.

Steam temperature control by means of water distribution can only be employed to decrease the steam temperature, never to increase it. Furthermore when this type of steam temperature control is used on reheaters it has a deleterious effect on the cycle efliciency since the spray water is not only bypassing the evaporative section but the entire high pressure turbine as well.

The method of exchanging heat between the various fluids in the vapor generator has been used to a limited extent. Since each of the fluids involved is a high pressure fluid, these heat exchangers require design for high pressures on both the heated and heating side. This presents diflicult design problems particularly on the shell side of a shell and tube heat exchanger. Furthermore heat exchangers of this type present considerable difliculties with respect to design for controllability. The pressure drop, the temperature head, and the film conductances must be considered in these heat exchangers throughout the operating control range. Where control of these heat exchangers by means of bypass flow is employed, it is extremely diflicult to obtain any reasonable controllability with-out incurring very high pressure drops. Where control by temperature head is used, desuperheaters must be employed to vary the temperature head. In either case a diflicult design problem evolves from this concept since we must deal with these high pressure surfaces over a considerable control range and are therefore severely restricted in the disposition of heating surface. The flexibility of this type design in regard to its ability to control temperature is severely restricted not only in direction of heat transfer but also as to magnitude.

In my invention a heat exchanger fluid at low pressure is circulated in heat exchange relationship with those fluids whose temperatures are to be controlled, whereby a simpler, more flexible, and more controllable steam temperature control system is evolved.

It is an object of this invention to provide an improved method of steam temperature control in a vapor generator.

It is a further object to provide a method of controlling a steam temperature in a vapor generator which has increased flexibility.

It is a further object to provide a method of steam control in a vapor generator which permits a'simplified pressure part design of the vapor generator.

Other and further objects of the invention will become apparent to those skilled in the art as the description proceeds.

With the aforementioned objects in view, the invention comprises an arrangement, construction and combination of the elements of the inventive organization in such a manner as to attain the results desired, as hereinafter more particularly set forth in the following detailed description of an illustrative embodiment, said embodiment being shown by the accompanying drawing wherein:

FIGURE 1 is a diagrammatic representation of a double (reheat power plant system wherein the instant invention is employed to control fluid temperatures within the vapor generator; and

FIGURE 2 is a diagrammatic representation of a single reheat cycle wherein a second embodiment of the instant invention is employed to control the fluid temperatures within the vapor generator.

Referring to FIGURE 1 booster pump 2 supplies water from condenser 3 through the low pressure feedwater heaters 4 to the high pressure feed pump 5. This high pressure feed pump supplies water at high pressure through the high pressure feedwater heaters 6 to the economizer 7 of the vapor generator. The temperature of the water entering the vapor generator would normally be in the order of 450 F. After initial preheating in the economizer 7 the water is evaporated in evaporating stage 8 (the economizer 7 and evaporating stage 8 comprising the evaporative section) and superheated in a first superheating stage 9 to about 850 F. Injection water 10 for steam temperature control is introduced desuperheating the steam before final superheating stage 12. The first superheating stage 9 and the final superheating stage 12 comprise the steam superheating section. The steam is then conveyed through the turbine throttle valve 13 to the high pressure steam turbine 14. The steam leaving the turbine is then conveyed to the boiler at a temperature of about 600 P. where it is reheated in high pressure reheater (or first steam reheating section) 15, after which it is delivered to the intermediate pressure turbine 17. The steam leaving this intermediate pressure turbine is then conveyed at about 600 F. to the low pressure reheater (or second steam reheating section) 18 where its temperature is again increased and it is delivered to the low pressure turbine 19. The steam leaving the low pressure turbine is condensed in condenser 3 and recycled through the power plant system.

Heat exchanger 22 is placed in the feedwater line ahead of the economizer 7 to add heat to the water passing therethrough. Placing the heat exchanger in this location, rather than farther downstream in the evaporating section, increases the temperature head available for heat transfer. After the superheating stage 9 and ahead of the injection point 10 heat exchanger 23 is placed to withdraw heat from the steam passing therethrough. A third heat exchanger 24 is placed ahead of the high pressure reheater to add or withdraw heat from the steam passing therethrough, and heat exchanger 25 is placed ahead of the low pressure reheater 18 in a similar manner. Circulating pump 26 is arranged to circulate a heat exchange fluid through the heat exchangers 22, 23, 24 and 25. Any fluid having high temperature stability such as biphenyl or compressed carbon dioxide may be used as the heat exchange fluid being pumped through the 'heat exchangers. Some fluids such as biphenyl which have high melting temperatures would require special design considerations to permit draining of the loops or electrical heating of the pipes to avoid freezing at normal ambient temperatures when the unit is shutdown.

The heat exchange fluid is pumped from the pump 26 through line 27 from where it may be conveyed through the heat exchanger 22 and through the cold line 23, or through the line 29 to heat exchanger 23 and the hot line 30. Valves 31 and 32 regulate the amount of flow passing through the heat exchanger 22 while valves 33 and 34 regulate the amount of flow passing through the heat exchanger 23. Valves 31 and 33 may be operated concurrently or independently to regulate the temperature of the fluid passing into line 35 which supplies the heat exchanger controlling the low pressure reheater 18 steam temperature. Valve 41 may be operated to control the flow passing through this line.

Valves 32 and 34 may be operated concurrently or independently to control the temperature of the fluid passing into line 37, from which point the fluid may be returned directly to the circulating pump 26 through valve 40, or the fluid may be conveyed through line 38 to the heat exchanger 24 controlling the temperature of the steam leaving the high pressure reheater 15, with valve 42 being operative to control the flow through this heat exchanger.

This apparatus is capable of a number of modes of operation. The system may operate to reduce superheated steam temperature by conveying heat from the superheater section to the evaporator section. To obtain this operation valves 41, 42, 31 and 33 should be closed, with valves 32, 34, and 4t) open. Flow will pass from pump 26 through the heat exchanger 22 giving heat to the water resulting in cold line 28 while a parallel flow path will pass through heat exchanger 23 removing heat from the steam resulting in the hot line 30. These two lines will join producing a mixed temperature in the line 37, this fluid being recycled to again add heat to the water passing through heat exchanger 22 and to extract heat in heat exchanger 23 from the steam passing therethrough. The amount of heat transferred would be varied to obtain the desired steam temperature by throttling valve 40 thereby regulating the amount of flow through the loop. Inasmuch as during equilibrium operation of the heat exchange fluid loop the amount of heat picked up by the heat exchanger 22 must equal the amount of heat lost by the heat exchange fluid in heat exchanger 23, the temperature of the fluid being pumped by pump 26 and passing through valve 40 to line 27 must be intermediate the water temperature entering heat exchanger 22 (450 F.) and the temperature of the steam entering the heat exchanger 23 (850 F.). The actual equilibrium temperature at which this loop will settle out will depend on the amount and effectiveness of the surface in the respective heat exchangers.

A second mode of operation can be employed Where there is excess superheat temperature and a deficiency in the high pressure reheat temperature. In this mode of operation valves 31, 32, 33, 4d and 41 would be closed with valves 34 and 4-2 being opened. Flow is passed from pump 26 through heat exchanger 23 and thence serially through line 38 and heat exchanger 24, returning through valve 42 to the pump. The amount of heat transferred is regulated by throttling valve 42 or 34 thereby varying the amount of flow through the heat exchange loop. In the event that the heat transfer characteristic is such that poor controllability results, partially opening valve 40 will increase the flow through heat exchanger 2-3. This will result in a changed operating temperature of the heat exchange fluid throughout not only lines 29 and but also in line 38, and therefore change the heat exchange characteristics of each heat exchanger.

Heat may similarly be transferred from the superheated steam through heat exchanger 23 to the low pressure reheater 18 through heat exchanger 25. For this mode of operation valves 31, 32, 34, 4t) and 42 would be closed with valves 33 and 41 being open.

In the event that the temperature of the superheated steam is essentially satisfactory, but the temperature of the steam leaving the high pressure reheater is excessive heat may be transferred from the reheater section to the evaporator section. In this mode of operation valves 31, 33, 34, 4t and 41 would be closed, with valves 32 and 42 being opened. The heat exchange fluid would be passed serially through heat exchanger 22, through lines 28 and 38, heat exchanger 24, valve 42 and pump 26. The amount of heat transfer is again controlled by varying flow used in this instant valve 42 as a throttling valve. If again the heat transfer characteristic of the heat exchangers is poor, valve 40 may be partially opened thereby increasing the flow through heat exchanger 22 and depressing the average of the heat exchange fluid.

Similarly heat may be transferred from the low pressure reheater 18 through heat exchanger 25 to the feedw-ater through heat exchanger 22. In this mode of operation valves 32, 33, 34, 40 and 42 would be closed with valves 31 and 41 being open. Flow of the heat exchange fluid will then pass serially through heat exchangers 22 and 25, the amount of flow being regulated by throttling valve 41. If it is desirable to change the heat transfer characteristic of the loop, valves 32 and 40 may be partially opened thereby again decreasing the average temperature of the heat exchange fluid.

Combinations of the aforementioned modes of operation can be employed simultaneously as desired. For instance, heat may be transferred from the superheated steam by heat exchanger 23 to both the high pressure reheater through heat exchanger 24 and the primary fluid through heat exchanger 22. For this mode of operation valves 31, 33, 41 and 40 would be closed with valves 32, 34, and 42 being .open. The heat exchange fluid then passes in parallel through heat exchangers 22 and 23 adding heat to the primary fluid in heat exchanger 22 and removing heat from, the steam in heat exchanger 23. The fluids thereafter join in passing through valves 32 and 34, the mixed fluid passing through line 38 to heat exchanger 24 where heat may be added to or taken from the reheat steam passing therethrough, the heat exchange fluid then passing out through valve 42 to be recirculated. Valves 32 and 34 may be regulated to vary the flow through heat exchangers 22 and 23 respectively and therefore the amount of heat transferred in each of these. Valve 42 may be operated to regulate the amount of flow through the system, while valve 40 may be partially opened so that the amount of flow passing in parallel through heat exchangers 22 and 23 is greater than that passing through the exchanger 24, thereby effecting the characteristics of each of the heat exchangers.

Another possible combination Would involve the transfer of heat from the high pressure reheater-section to the evaporator section simultaneously with transfer of heat from the superheated steam to the low pressure reheater. To entertain this mode of operation valves 31, 34 and 40 would be closed while valves 32, 33, 41 and 42 would be open. The heat exchange fluid would be pumped through heat exchanger 22 where heat was added to the .boiler feedwater, thence through line 28, valve 32 and line 38 to heat exchanger 24 where heat would be taken from the steam. The heat exchange fluid is then conveyed through valve 42 to return to the circulating pump 26. Simultaneously the heat exchange fluid to be circulated by pump 26 is delivered through line 29 .to heat exchanger 23 where heat is removed from the superheated steam. The fluid continues through line 30, valve 33 and line 35 to heat exchanger 25 where heat is given to the steam entering the low pressure reheater 18. The fluid is then conveyed through valve 41 returning to pump 26. Valve 42 controls the flow through heat exchanger 24 and therefore the temperature of steam leaving the high pressure reheater 15, While valve 41 controls the flow of the fluid through the heat exchanger 25 and therefore the temperature of the steam leaving the low pressure reheater 18.

Heat may be transferred from the super-heated steam by heat exchanger 23 to both the high pressure reheater through heat exchanger 24 and the low pressure reheater selectively to heat exchangers 24 and 25, by operation of valves 33 and 34. These valves may be operated to regulate the amount of flow through the system, while valve 40 may be partially opened so that the amount of flow passing through heat exchanger 23 is greater than that passing in parallel through the exchangers 24 and 25, thereby effecting the characteristics of each of the heat exchangers.

FIGURE 2 is a diagrammatic representation of a similar turbine plant cycle having a single reheat wherein the feedwater system and the steam generator primary side are similar to FIGURE 1. Steam leaving the high pressure turbine 14 passes through reheater 50 to reheat turbine 51 whereupon the fluid is condensed in condensor 3 and recycled.

Heat exchanger 52 is installed in the feedw-ater supply leading to the economizer 7 while heat exchanger 53 is installed in the steam line conveying steam from the superheater 9 to the final superheater 12. It is advantageous to locate this heat exchanger upstream of location where injection water 10 is supplied for desuperheating, to obtain the maximum available steam temperature through heat exchanger 53 and therefore the maximum available temperature head between the steam and the heat exchange fluid. Heat exchanger 54 is located in the reheat steam line supplying steam to the reheater 50.

Heat exchange fluid is circulated by circulating pump 56 either through heat exchanger 52 passing through valve 60 or bypassing the heat exchanger through valve 61. This fluid then continues passing through heat exchanger 53 through valve 62 or bypasses the heat exchanger through valve 63. The heat exchange fluid completes its loop by returning to pump 56 either through heat exchanger 54 through valve 64, or bypassing heat exchanger 54 through valve 65.

Where heat is to be exchanged between the superheater section and the evaporator section valves 61 and 63 and 64 are closed, while valves 60, 62 and 65 are open. The fluid is then recirculated serially through heat exchangers 52 and 53 passing through the open valves transferring heat between the superheated steam and the incoming feedwater. The amount of heat to be transferred is con trolled by regulating the flow in the recirculating loop by throttling any one of the open valves.

Heat may be transferred from the superheated steam to the reheat steam by closing valves 60, 63 and 65 with valves 61, 62 and 64 being open. Heat is similarly transferred from the steam passing through heat exchanger 53 to the reheat steam passing through heat exchanger 54, control again being by throttling any one of the open valves.

Heat may be transferred from the reheat steam to the evaporator section by opening valves 60, 63 and 64 with valves 61, 62 and 65 being closed. The flow similarly transfers heat between the feedwater supply and the reheat steam with control again being by means of throttling any one of the open valves.

Heat may also be transferred from the superheated steam to both the reheat steam and the evaporator section. The basic flow pattern is obtained by closing valves 61, 63 and 65 with valves 60, 62 and 64 being opened. With this arrangement the flow passes serially through all the heat exchangers. The heat given to the feedwater may be controlled by regulating bypass valve 61, while the amount of heat transferred to the reheat steam may be regulated by controlling bypass valve 65. The temperature level of the operating fluid may be controlled by manipulating superheat heat exchanger 53 bypass valve 63.

While I have illustrated and described a preferred embodiment of my invention it is to be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein without departing from the spirit and scope of the invention.

I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes as fall within the purview of my invention. For instance, the primary fluid heat exchanger may be located after the economizer or in the evaporating section, instead of upstream of the economizer. The heat exchanger in the reheat line may be located at a point where the reheat steam temperature is higher than the superheat temperature, wherein a similar design philosophy as described in the foregoing embodiments would be applied. Where only one mode of operation is desired, only a portion of the described apparatus need be installed. This invention is equally applicable to once-through boilers of both the supercritical and subcritical type.

What I claim is:

1. In a vapor generator having a plurality of heating sections, each section having at least one heating stage located within the vapor generator, and having supply means to each stage located outside the vapor generator, the improvement comprising: heat exchange means located in at least three of the sections in the supply means outside of the vapor generator; means for conveying a heat exchange fluid through one of said heat exchangers to establish a cold stream of heat exchange fluid; means for conveying heat exchange fluid through a second of said heat exchangers to establish a hot stream of heat exchange fluid; means for selectively supplying heat exchange fluid from the first and second heat exchangers to the third of said heat exchangers; and means for eflecting circulation of the heat exchange fluid.

2. An apparatus as in claim 1 including also means for bypassing the heat exchange fluid around said third heat exchanger.

3. In a vapor generator having an evaporator section having heating stages located within the vapor generator and supply means iocated outside the vapor generator serially connecting the heating stages; a superheating section having superheating stages located inside the vapor generator, and having supply means located outside the vapor generator serially connecting said superheating stages, a reheating section having a reheating stage located within the vapor generator and supply means for the reheating stage located outside the vapor generator, the improvement comprising: a heat exchanger located in the superheating section in the supply means located outside the vapor generator; a heat exchanger located in the reheating section in the supply means located outside the vapor generator; means for circulating heat exchange fluid serially through said heat exchangers; and means for eflecting recirculation of the heat exchange fluid.

4. In a vapor generator having an evaporator section having heating stages located Within the vapor generator and supply means located outside the vapor generator connecting the heating stages; a superheating section having superheating stages located inside the vapor generator, and having supply means located outside the vapor genertor supplying said superheating stages, a reheating section having a reheating stage located within the vapor generator and supply means for the reheating stage located outside the vapor generator, the improvement comprising: a heat exchanger located in the evaporator section in the supply means outside the vapor generator; a heat exchanger located in the superheater section in the supply means outside the vapor generator; a heat exchanger located in the reheate-r section in the supply means located outside the vapor generator; means for recirculating heat exchange fluid serially through said heat exchangers; and means for effecting the recirculation of the heat exchange fluid.

'5. In a vapor generator having an evaporator section having heating stages located Within the vapor generator and supply means located outside the vapor generator connecting the heating stages; a superheating section having superheating stages located inside the vapor generator,

and having supply means located outside the vapor generator supplying said superheating stages; a reheating section having :a reheating stage located within the vapor generator and supply means for the reheating stage located outside the vapor generator, the improvement comprising: a first heat exchanger located in the evaporator section in the supply means outside the vapor generator; a second heat exchanger located in the superl eater section in the supply means located outside the vapor generator; a third heat exchanger located in the reheater section in the supply means located outside the vapor generator; means 'for conveying heat exchange fluid in parallel through said first and second heat exchangers; means 'for conveying the fluid selectively from said first and second heat exchangers through said third heat exchanger; and means for effecting recirculation of the heat exchange fluid through said heat exchangers.

6. An apparatus as in claim '5 including also means for bypassing the heat exchange fluid around said third heat exchanger.

7. In a vapor generator having an evaporator section comprising heat stages inside the vapor generator and supply means outside the vapor generator supplying each of the stages, a superheating section saving superheating stages inside the vapor generator and supply means located outside the vapor generator to supply the superheating stages, a first reheating section inside the vapor generator and the supply means outside the vapor generator to supply the reheating stage, a second reheating section having a reheating stage inside the vapor generator and supply means located outside the vapor generator to supply the reheating stage, the improvement comprising: a first heat exchanger in the evaporator section located in the supply means outside the vapor generator; a second heat exchanger located in the superheater section located in the supply means outside the vapor generator; a first reheat exchanger in the first reheater section located in the supply means outside the vapor generator; a second reheat heat exchanger located in the second reheat section till the supply means outside the vapor generator; means for conveying heat exchange fluid through a first path comprising said first heat exchanger and one of said reheat heat exchangers serially; means for conveying heat exchange fluid through a second path comprising said second heat exchanger and the other reheat heat exchanger serially; means for recirculating heat exchange fluid through the two flow paths in parallel.

8. In a vapor generator having a superheater section comp-rising zfluid heating stages and means for supplying said stages located outside the vapor generator, a reheating section comprising a reheating stage located inside the vapor generator and supply means located outside the vapor generator to supply said reheating stage, the improvement comprising: a heat exchanger located in the superheater section in the supply means located outside the vapor generator; a heat exchanger located in the reheating section in the supply means located outside the vapor generator; and means for effecting the circulation of heat exchange fluid serially through said heat exchangers.

9. In a vapor generator having an evaporator section comprising fluid heating stages and means for supplying said stages located outside the vapor generator, a reheating section comprising a reheating stage located inside the vapor generator and supply means located outside the vapor generator to supply said reheating stage, the improvement comprising: a heat exchanger located in the evaporator section in the supply means located outside the vapor generator; a heat exchanger located in the reheating section in the supply means located out- ,side the vapor generator; and means for effecting the circulation of heat exchange fluid serially through said heat exchangers.

10. In a vapor generator having an evaporator section having heat stages located within the vapor generator and supply means located outside the vapor generator serially connecting the heating stages; a superheating section having superheating stages located inside the vapor generator, and having supply means located outside the vapor generator serially connecting said superheating stages; a [first reheating section having a reheating stage located within the vapor generator and supply means for the reheating stage located outside the vapor generator; and a second reheating section having a reheating stage located Within the vapor generator and supply means for the reheating stage [located outside the vapor generator; the improvement comp-rising: a superheat heat exchanger located in the superheating section in the supply means located outside the vapor generator; a first reheat heat exchanger located in the first reheating section in the supply means located outside the vapor generator; a second reheat heat exchanger located in the second reheating section in the supply means located outside the vapor generator; means for conveying heat exchange fluid through the superheat heat exchanger; means for conveying the heat exchange fluid selectively from the superheat heat exchanger to the reheat heat exchangers in the desired proportions; and means for effecting recirculation of the heat exchange fluid.

11. The method of regulating vapor temperature in a vapor generator comprising: heating a vaporizable fluid in a plurality of heating sections; passing a non-vaporizing heat exchange fluid in heat exchange relationship With the vaporizable fluid of a first of the heating sections; conveying the heat exchange fluid to a second of the heating sections of the vaporizable fluid; passing the heat exchange fluid in heat exchange relationship with the vaporizable fluid of the second heating section; conveying the heat exchange fluid to the first heating section to be again passed in heat exchange relationship with the vaporizable fluid; determining the temperature of the vaporizable fluid leaving one of said heating sections and regulating the quantity of flow of the heat exchange fluid in direction and magnitude to control said determined temperature to a desired value.

12. The method of controlling vapor temperature in a vapor generator comprising: heating a vaporizable fluid in an evaporating section; superheating the vaporizable fluid in a superheating section; extracting work from the vapor in a vapor turbine; reheating the vapor in a reheating section; passing a non-vaporizable heat exchange fluid in heat exchange relationship with the vaporizable fluid of the evaporating section, thereby forming a cold stream; passing non-vaporizable heat exchange fluid in heat exchange relationship with the vapor of the superheating section, thereby forming a hot stream; mixing the hot and cold streams; passing the mixed heat exchange fluid in heat exchange relationship with the vapor of the reheating section; returning the heat exchange fluid to be passed in heat exchange relationship with the evaporating and superheating sections again; and regulating the proportion of the hot and cold streams to control the vapor temperature of the vaporizable fluid leaving the reheater.

13. The method of controlling vapor temperature in a vapor generator comprising: evaporating a vaporizable fluid in an evaporating section; superheating the vaporizable fluid in a superheating section; utilizing energy of the vapor in a vapor turbine; reheating the vapor leaving the vapor turbine in a reheating section; passing a non-vaporizing heat exchange fluid in heat exchange relationship with the vaporizable fluid of the superheating section; then passing this heat exchange fluid in heat exchange relationship with the vaporizable fluid of the reheating section; recycling the heat exchange fluid to again pass in heat exchange relationship with the vaporizable fluid in the superheating section; determining a temperature of the vaporizable fluid after its passage in heat exchange relationship with the non-vaporizing heat exchange fluid; and controlling the temperature of the fluid so determined by regulating the quantity of flow of the heat exchange fluid.

14. A method of controlling vapor temperature in a vapor generator comprising: evaporating a vaporizable fluid in an evaporating section; then superheating the vaporizable fluid in a superheating section; extracting en ergy from the vapor in a vapor turbine; reheating the vapor in a first reheating section; extracting additional work from the vapor in a vapor turbine; again reheating the vapor in the second vapor reheating section; passing a non-vaporizable heat exchange fluid in heat exchange relationship with the vaporized fluid of the superheating section; passing the heat exchange fluid in heat exchange relationship with the vapor of both of the reheating sections in parallel; and selectively proportioning the heat exchange fluid passing in heat exchange relationship with the vapor of each of the reheating sections to control the vapor temperature of the steam being reheated.

References Cited by the Examiner UNITED STATES PATENTS 1,889,586 11/1932 Grebe 12233 X 1,895,220 1/1933 Grebe 122-1 X 1,912,938 6/1933 Grebe 1221 CHARLES I. MYHRE, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,260,244 July 12, 1966 Henry J. Blaskowski It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 34, for "temperature" read temperatures lines 44 and 45, for "section is independent, its heat re quirements being dicto the desired temperature. In heat units each reheater" read to the desired temperature. In reheat units each reheater section is independent, its heat requirements being dicline 51, for "neat" read heat same column 1, line 71, for "mehods" read methods column 2, lines 65 and 66, after "generator." insert the following paragraph:

It is a further object to provide a low pressure circuit conveying heat exchange fluid to transfer heat from one section of the vapor generator to the other.

Column 8 line 22, and column 9, line 1, for "heat", each occurrence, read heating column 8, line 37, after "reheat" insert heat column 9, lines 47 and 50, and column 10, line 35, for "non-vaporizable", each occurrence, read nonvaporizing Signed and sealed this lst day of August 1967.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. IN A VAPOR GENERATOR HAVING A PLURALITY OF HEATING SECTIONS, EACH SECTION HAVING AT LEAST ONE HEATING STAGE LOCATED WITHIN THE VAPOR GENERATOR, AND HAVING SUPPLY MEANS TO EACH STAGE LOCATED OUTSIDE THE VAPOR GENERATOR, THE IMPROVEMENT COMPRISING: HEAT EXCHANGE MEANS LOCATED IN AT LEAST THREE OF THE SECTIONS IN THE SUPPLY MEANS OUTSIDE OF THE VAPOR GENERATOR; MEANS FOR CONVEYING A HEAT EXCHANGE FLUID THROUGH ONE OF SAID HEAT EXCHANGERS TO ESTABLISH A COLD STREAM OF HEAT EXCHANGE FLUID; MEANS FOR CONVEYING HEAT EXCHANGE FLUID THROUGH A SECOND OF SAID HEAT EXCHANGERS TO ESTABLISH A HOT STREAM OF HEAT EXCHANGE FLUID; MEANS FOR SELECTIVELY SUPPLYING HEAT EXCHANGE FLUID FROM THE FIRST AND SECOND HEAT EXCHANGERS TO THE THIRD OF SAID HEAT EXCHANGERS; AND MEANS FOR EFFECTING CIRCULATION OF THE HEAT EXCHANGE FLUID. 